1. Field of the Invention
This invention pertains to a process and an apparatus for the control of a hydraulic lift wherein a control device produces control signals that are directed to a regulation valve arrangement which in turn so controls the through-flow of fluid under pressure that an elevator car is accelerated, moves with a constant velocity and thereafter decelerates upon the arrival of a shaft information signal which in turn produces a brake-input or slow down initiation point.
2. Discussion of the Background of the Invention and Material Information
In such lifts, the drive Velocity depends more or less strongly on variations in car load and the temperature of the hydraulic pressure medium, whereby the hydraulic pressure flow, controlled via a regulation valve, changes correspondingly so that an exact floor approach is not possible. In order to correct this deficiency, shortly prior to the arrival at the floor, the velocity is switched to a small, constant creeping or levelling speed, so that the height difference, caused via load and/or temperature changes, can be compensated (see prior art FIG. 3). This, in turn, leads to increasing operating and waiting times for users and requires high energy usage in hydraulic lifts, in addition and as is well known, the length of the creeping speed is also dependent upon load and temperature conditions.
German Patent Publication DE 36 38 247 teaches an apparatus for a hydraulic lift according to which the previously noted deficiencies are to be eliminated. This apparatus utilizes a control device that produces output signals defined by the velocity behavior of the lift, with these output signals then being directed to a control valve. The control valve, in turn, channels pressurized fluid, from a source of fluid pressure, to or from a hydraulic drive cylinder, in accordance with these output signals. In a memory unit, connected with the control device via a computer, reference velocity values are stored, which values correspond with defined operating condition, which in turn are based upon differing load and/or temperature relationships. A sensing element attached to the car obtains the actual velocity and channels same, via a converter system, to the computer. Therewith, a difference is obtained between the actual velocity, measured during the acceleration phase, and a predetermined reference speed, based upon which the computer calculates a control velocity curve. This curve, in turn, is stored and then utilized during the deceleration phase to correct the actual velocity to, the value of the previously-mentioned reference velocity. In this manner, an exact and quick approach to designated areas is to be achieved and the operating time of the lift is to be reduced. However, this control device, even though not utilizing a control circuit or control for the adaptation of the slow down initiation point, cannot operate without the use of a creeping or levelling speed.